Nano: not in sync error

After days of putting up this power supply board with everything soldered together. Now being happy and all after long working hours, I wrote a testing code for the board, and suddenly I got this error.

avrdude: stk500_getsync(): not in sync: resp=0x00

I know it means that my pc is not communicating with my arduino. but why? what is possibly the cause for this error?

I know it is not the problem from: 1, usb driver; 2, software; 3, the code; and I have not connected anything to pin tx, and rx.

there are my pin layout:
13 Sck
11 SI
Outpin 10: CS Digital Potentiometer enable Pin
Outpin 9: swtich P-fet (Power OutPut)
Outpin 8: swtich NPF (discharger)
A0: button OK (Digital)
A1: Button → (Digital)
A2: Button <+ (Digital)
A3: Shunt Voltage (Analog)
A4: Temp Sensor (Analog)
A5: Battery Voltage (Analog)
A6: Power out Voltage (Analog)
A7: Discharge Battery Voltage (Analog)
LiquidCrystal lcd(2,3,4,5,6,7);

did you try pushing the reset button just before you upload?

BulldogLowell: did you try pushing the reset button just before you upload?

i did. I also checked all the pin with my mulitmeter. reset pin is connected to nothing but the onboard reset button. double check again, tx, rx is not connected to anything. This same board, before assemble, has been tested, and it worked, but won't work now!

I had the exact same problem with mine. Everyone said make sure you chose nano in your boards selection..... Anyway after months of trial and error, I threw it away.

ben_meyer:
I had the exact same problem with mine. Everyone said make sure you chose nano in your boards selection… Anyway after months of trial and error, I threw it away.

that is sad. I think deep deep down, your nano has feeling just like you do. and abandon it like that is just sad.

Take a look in the Installation & Troubleshooting forum. THIS IS NOT A PROGRAMMING PROBLEM. You have the wrong comms port selected in the IDE.

Mark